16 Alzet, model 2006 miniature osmotic pumps (Durect Corporation, Cupertino, CA) were loaded with mouse recombinant IL-4 (R&D Systems, Minneapolis, MN) at a concentration of 2 µg/ml diluted in carrier solution comprising of 1% bovine serum albumin (BSA, Sigma-Aldrich, St. Louis, MO) and phosphate buffered saline (PBS). 5 additional pumps were loaded with IL-4 with carrier solution and 15 mg/ml UHMWPE particles (mean diameter 1µm ± 0.1 µm as assessed by electron microscopy) isolated from knee replacement simulators as previously described [22 (link)]. The particles were tested negative for endotoxin using Limulus Amebocyte Lysate Kit (BioWhittaker, Walkersville, MD). Pumps were connected via 6cm long vinyl tubing (Durect Corporation), pre-filled with their corresponding solutions, to a collection vessel containing 500µl of a mouse bone marrow macrophage (mBMM) augmented media. The whole assembly was placed inside 50ml centrifuge tube partially filled with PBS, and then incubated at +37°C for 4 weeks. The conditioned mBMM media was initially collected at day 3, 5 and 7 after the beginning of the infusion and then at seven day intervals (week 1, 2, 3 and 4 samples) with fresh media added to the collection vessel after each sample collection. Conditioned media was stored at −80°C until used for subsequent experiments.